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Re: Polar Alignment scope & GM-8 mount


Mar 11, 2007

 


----------------------------

#32325 Mar 11, 2007

Hi all,



I'm back with more questions. This time it concerns the proper

installation to the polar alignment scope in a GM-8 mount. I plan to

use the mount for imaging.



1) I've been told by a friend that you have to align the reticle in the

alignment scope and then align the scope to the mount. Is this true?



2) If so, how critical is this and what is the best procedure?



3) Once the polar scope is installed in the GM-8, can I leave it in? I

have to transported the mount and set-up each time I use it. How safe

would leaving the scope in the mount be?



Any help with the above questions would be appreciated.





Thanks, and clear skies,

Mike T



----------------------------

#32327 Mar 11, 2007

The polar scope is installed by replacing the cap in place right now with

the polar scope that just threads in with a collar.



To polar align, you have to rotate the polar scope so that the star field in

the reticle is the same orientation as the actual star field you are seeing

right now ( align the reticle in the alignment scope?)



Then you just use the polar scope to align the mount.



Most of the polar scope is inside the mount, with maybe 2 inchs sticking out

the back. I routinely transport my GM8 with polar scope attached with no

problems.



Hope this helps

Vincent

On 3/11/07, tapsky01 tapsky@...> wrote:

>

> Hi all,

>

> I'm back with more questions. This time it concerns the proper

> installation to the polar alignment scope in a GM-8 mount. I plan to

> use the mount for imaging.

>

> 1) I've been told by a friend that you have to align the reticle in the

> alignment scope and then align the scope to the mount. Is this true?

>

> 2) If so, how critical is this and what is the best procedure?

>

> 3) Once the polar scope is installed in the GM-8, can I leave it in? I

> have to transported the mount and set-up each time I use it. How safe

> would leaving the scope in the mount be?

>

> Any help with the above questions would be appreciated.

>

> Thanks, and clear skies,

> Mike T

>

>

>





[Non-text portions of this message have been removed]



----------------------------

#32328 Mar 11, 2007

Vincent.



Thanks for the reply. I understand how to attach and use the polar

scope. It's the alignment of the reticle within the polar scope

itself I'm refering to. I guess the reticle can be shipped without be

properly centered in the scope, at least that's what was implied in a

friends comment.



Glad to hear you can keep the scope installed in the mount without

problems.



Mike



----------------------------

#32338 Mar 12, 2007

On 12 Mar 2007 11:51:44 -0000, Losmandy_users@yahoogroups.com wrote:



Mike, with four polar scopes so far that I've worked on, mine included, the

reticle is not centered in the bore of the scope. You can prove it to yourself by

installing the scope in the bore of the GM-8 and using the elevation adjusters to

lower the altitude so that the axis is closer to level or the horizon. Use

something in the distance like a power pole insulator as your target. Then

rotate the scope in the bore. You will see the center intersection of the long

three lines not rotating concentrically around the target. You will need to find

a 0.035" allen key (very tiny) to adjust the reticles 3 alignment set screws in

the barrel. Loosen two, tighten one.... loosen one, tighten two, etc. Be very

careful in tightening the set screws, do not apply excessive pressure. If you

need to go further in a direction, loosen enough on the other side. You can put

so much pressure on the reticle cell that you can crack or chip the glass reticle

because the small set screws can supply great force over a small area.

Shouldn't take more that 15-30 minutes to align the reticle. Once done, you can

expect to consistently achieve A&E values of 1-2 arc-minutes or better for your

polar alignment. As long as you put all three stars at their alignment points

when you use your adjusters, you will get a polar alignment good enough for

imaging without drift alignment.



Keith



>Vincent.

>

>Thanks for the reply. I understand how to attach and use the polar

>scope. It's the alignment of the reticle within the polar scope

>itself I'm refering to. I guess the reticle can be shipped without be

>properly centered in the scope, at least that's what was implied in a

>friends comment.

>

>Glad to hear you can keep the scope installed in the mount without

>problems.

>

>Mike

PMMail/2 Tag->Keith Myers.... computing into the future with eComStation!



This OS/2 system uptime is 0 days 06:54 hours (en).



----------------------------

#32339 Mar 12, 2007

Keith,



Thanks for the reference. I'll check it out.



Mike



[Non-text portions of this message have been removed]



----------------------------

#32340 Mar 12, 2007

Mike - I'm not sure but it may be that the "alignment" you are

speaking of has to do with the angular position of the reticle.



If you look in the polar scope the reticle has, among other things,

two constellations engraved on it. They are Ursa Major (Big Dipper),

and Cassiopia. One or the other, or both, of these will be visible in

the sky at any given time. You need to rotate the reticle (it rotates

in it's mount) so the position of these constellations (angular

position, ie one o'clock, six o'clock, or whatever) are as close as

you can match to where they are in the sky at the time. Mind you, the

connstellations themselves will not be visible in the polar scope, the

field of view is too small. But the angular position of their etching

on the reticle needs to match where they are in the sky.



Then, the three stars, including polaris, you use to align the mount

will be close to where they need to be for the actual alignment and

you can identify them. Quite often only two of the three, including

polaris, will be visible because the third is pretty faint. Two is

enough.



The Losmandy web site has a PDF that explains all this.



Pat

--- In Losmandy_users@yahoogroups.com, "tapsky01" tapsky@...> wrote:

>

> Vincent.

>

> Thanks for the reply. I understand how to attach and use the polar

> scope. It's the alignment of the reticle within the polar scope

> itself I'm refering to. I guess the reticle can be shipped without be

> properly centered in the scope, at least that's what was implied in a

> friends comment.

>

> Glad to hear you can keep the scope installed in the mount without

> problems.

>

> Mike

>







----------------------------

#32342 Mar 12, 2007

Hi all,

>

> I'm back with more questions. This time it concerns the proper

> installation to the polar alignment scope in a GM-8 mount. I plan to

> use the mount for imaging.

>

> 1) I've been told by a friend that you have to align the reticle in the

> alignment scope and then align the scope to the mount. Is this true?

> 2) If so, how critical is this and what is the best procedure?

Many people will simply fit the scope, and not bother to 'align' it

further. However what he is probably talking about, is centering the

reticle. You can aim the scope at am object (typically put Polaris on the

centre hair, rather than it's normal 'alignment' position), and then rotate

the whole scope. If the scope is properly centred, the crosshair should

remain on the target. If not, then centreing the reticle may be worthwhile.

This is done with three tiny grub screws, and _must_ be done very gently.

You just fractionally slacken a screw, and tighten the next. Any force at

all, can crack the glass. Done properly, it improves the accuracy

achievable by the polar scope, but most are good enough out of the box, and

for really good polar alignment drift aligning will always be necessary, so

I'd say leave it alone...

In use, all you do is rotate the system to match the orientation of the

sky, and align the three stars in their respective gaps in the reticule.

The central crosshair, then points at the true 'north' point.

> 3) Once the polar scope is installed in the GM-8, can I leave it in? I

> have to transported the mount and set-up each time I use it. How safe

> would leaving the scope in the mount be?

Most people leave the scope in place. With the cover on, and the possibly

the illuminator removed.



Best Wishes



----------------------------

#32343 Mar 12, 2007

Pat, and others



Nope, I'm talking about the alignment of the reticule within the barrel of the polar scope itself.



I guess a better word would have been collimation rather than alignment. The reticule is adjustable within the scope's barrel. As I've learned from other replies (thanks to all who have replied by the way) the reticule is very fragile, and great care is needed in adjusting it.



Like so many things in amateur astronomy, the gear we buy is not perfect, and needs tweaking. I just wish manufactures owned up to this fact and included tweaking instructions with their products. I don't know about the rest of you, but I'd be willing to pay extra to get a pre-tweaked product I didn't have to worry with before use.



I mean think about this. I bought a Polar Alignment Scope to save time and aggravation in polar aligning the mount. Now I have to worry that the alignment scope is not aligned (collimated). That seems pretty dumb to me.



Sorry, just venting after a cold cloudy winter.



Clear skies,

Mike



[Non-text portions of this message have been removed]



----------------------------

#32344 Mar 12, 2007

Hi Mike,



You wrote,

>

> I mean think about this. I bought a Polar Alignment Scope to save

time and aggravation in polar aligning the mount. Now I have to worry

that the alignment scope is not aligned (collimated). That seems

pretty dumb to me.



Did you check it and you know wth certainty that it is not

collimated ?



If not, then why worry about it ?



As other have said it is very very delicate. A friend of mine whi

things that he has to adjust everything .....



Well the reticle looks like a glass garbage can ....



As it comes and other have already said it is for a first rough

aligment very good collimated already. If you are an imager you will

in anyway have to use all other tools which are rpesent in the Gemini

GoTo to get it nearly perfect polar aligned.



Using correctly the polar scope I alwasy achieve at first alignment

run values of less then 5 arcminutes which is quite good for a start.



With 2-3 additional PAC I achieve alignments under 30 arcseconds.



saludos Rainer



----------------------------

#32347 Mar 12, 2007

This is a tweak you're better off without (the polar scope reticule).

I have measured the polar alignment error of the scope (which has

some wobble) from 1-2 arc minutes to 10 arc minutes (as measured by

Argo Navis). The intrinsic wobble of the mounting is much worse than

anything yo0u can fix by adjusting the tiny reticule screws. And,

when you have the stars lined up inside the crosshairs, there will

still be slight night to night differences.



1-2 arc minutes error is within the measurement error of Argo Navis

with good setting circles and 10 arc minutes isn't a whole lot, so my

personal 2c is to put one's efforts elsewhere.



regards

Greg N





--- In Losmandy_users@yahoogroups.com, "Michael Tapper" tapsky@...>

wrote: >

> Pat, and others

>

> Nope, I'm talking about the alignment of the reticule within the

barrel of the polar scope itself. >

> I guess a better word would have been collimation rather than

alignment. The reticule is adjustable within the scope's barrel. As

I've learned from other replies (thanks to all who have replied by the

way) the reticule is very fragile, and great care is needed in

adjusting it. >

> Like so many things in amateur astronomy, the gear we buy is not

perfect, and needs tweaking. I just wish manufactures owned up to this

fact and included tweaking instructions with their products. I don't

know about the rest of you, but I'd be willing to pay extra to get a

pre-tweaked product I didn't have to worry with before use. >

> I mean think about this. I bought a Polar Alignment Scope to save

time and aggravation in polar aligning the mount. Now I have to worry

that the alignment scope is not aligned (collimated). That seems

pretty dumb to me. >

> Sorry, just venting after a cold cloudy winter.

>

> Clear skies,

> Mike

>

> [Non-text portions of this message have been removed]

>







----------------------------

#32348 Mar 12, 2007

Hi Mike,



FWIW, re: Losmandy polar scope reticle centering.



Its usually not that critical.



Many many times, I've simply eyeball centered Polaris through an open

bore-hole in a GM-8 and visually observed with relatively good

tracking never using the polar scope at all. It very much depends on

the focal length of the scope in use at the time. 800mm refractors,

usually no problem; 2350mm SCTs want more critical alignment via the

polar scope.



Over the years, I've centered 2 reticles. Its a delicate task, but

first you must determine if its even necessary and usually it really

isn't, IMHO.



I believe the reason that the reticle has adjustment is too allow for

manufacturing variances in the tolerances of the bore hole, i.e., a

few .001" here or there.



If imaging, whether the reticle was centered or not, I always drift

align after getting close with the reticle. Once you've drift aligned

enough, it doesn't take very long.



To determine if your reticle needs any adjustment, accurately drift

align, and then re-check your reticle to see the displacement error.

It may be so small that its not worth risking breaking your reticle.



If you decide to adjust it, first back off all 3 screws a whisker.

Then determine which direction you want to move the reticle and back

off the opposite side a 2nd whisker or two. Then gently adjust the

correct screw to move the reticle in the correct direction. Upon

feeling ANY pressure AT ALL, however light, STOP, and loosen the

other side another whisker immediately. Your tweaks will be very,

very minimal at all times. Your tiny allen wrench can apply a lot of

torque against something so fragile as the delicate reticle with

little effort. Always use the long side of the allen wrench in the PS

housing and turn the small side.



I have broken one reticle and ordered another from Scott so I tell

you this from experience on how to do it and that its usually not

needed. I like being anal and tweaking stuff so I couldn't resist

g>.



But I am not at all concerned about centering my current reticle

based on my experience and especially since my PS is shared between

two different mounts (GM-8 and MI-250). Centered in the housing is

good enough for visual use, and for imaging you're still gonna drift

align if not in a permanent set-up.



Jay



----------------------------

#32349 Mar 13, 2007

Jay,



Thanks for the detailed advise. I'll calm down as give the reticule another go today.



As usual, I just had to tweak things. And as usual my first attempt made things worse. At least the reticule is still intact.



Success in this hobby requires a large dose of humor!



Clear skies,

Mike



[Non-text portions of this message have been removed]



----------------------------

#32352 Mar 13, 2007

Just to be clear that we are talking about the same issue. I think I

misunderstood your "collimation" reference in an earlier post

relative to a previous experience of mine.



To check and center the reticle, if needed, in the PS in the daylight

by using a fixed target such as a telephone pole insulator is not

difficult at all. Just be very patient and have a light touch. See

the AP site's technical section for details.



But, I took it too far and then tried to verify whether a centered

reticle in the PS housing is also a "collimated" reticle to a

specific mount's manufacturing accuracy by drift aligning at night to

check any displacement error. This step is not necessary. Simply

centering the reticle on axis in the PS housing is plenty good

enough, IMO.













--- In Losmandy_users@yahoogroups.com, "Michael Tapper" tapsky@...>

wrote: >

> Jay,

>

> Thanks for the detailed advise. I'll calm down as give the reticule

another go today. >

> As usual, I just had to tweak things. And as usual my first attempt

made things worse. At least the reticule is still intact. >

> Success in this hobby requires a large dose of humor!

>

> Clear skies,

> Mike

>

> [Non-text portions of this message have been removed]

>



----------------------------

#32353 Mar 13, 2007

Jay



I'm happy to report that I got the reticule pretty well centered and can now move on to other things.



I'd like to thank you and all the others who offered help and advise with this issue.



Regards,

Mike



[Non-text portions of this message have been removed]



----------------------------

#32358 Mar 13, 2007

On 13 Mar 2007 11:48:37 -0000, Losmandy_users@yahoogroups.com wrote:



Greg, in my case (MI-250) there is no wobble or uncertainty in the alignment of

the scope becasue the scope is mounted off axis due the mount design. The

3-point dovetail scope holder that Mountain Instruments provides is able to hold

the polar scope alignment consistently. Whatever residual error in the mount

after PAC alignment is programmed into the polar scope and is eminently

repeatable. Because of Polaris' rotation around the pole throughout the year, if

the reticle is not concentrically aligned, you will not be able to do an accurate

polar alignment using just the scope. That is why I chose to align the reticle. It

was not hard to do and I have not broken a single reticle in the 3 others I have

aligned for friends. If you are just doing visual you might have an argument for

leaving things alone.



Keith



>This is a tweak you're better off without (the polar scope reticule).

> I have measured the polar alignment error of the scope (which has

>some wobble) from 1-2 arc minutes to 10 arc minutes (as measured by

>Argo Navis). The intrinsic wobble of the mounting is much worse than

>anything yo0u can fix by adjusting the tiny reticule screws. And,

>when you have the stars lined up inside the crosshairs, there will

>still be slight night to night differences.

>

>1-2 arc minutes error is within the measurement error of Argo Navis

>with good setting circles and 10 arc minutes isn't a whole lot, so my

>personal 2c is to put one's efforts elsewhere.

>

>regards

>Greg N

PMMail/2 Tag->Keith Myers.... computing into the future with eComStation!



This OS/2 system uptime is 0 days 22:23 hours (en).







----------------------------

#32372 Mar 15, 2007

Mmmmmmm.



Not so sure. The reticle misalignement may originate from two causes

that can combine:



1) the reticle is not centered with the polar scope optical axis

2) the polar scope is mechanically not aligned with the centerline of

the polar axis of the mount.



If you check the reticle with the polar scope installed in the mount

(by checking a target remains centered in the middle of the reticle

when rotatig the polar axis), you may reach a correct centering that

won't hold when you remove the polar scope and you put it back.



Both verifications should be done separately: first rotate the polar

scope into a kind of V shaped rail while aiming at a target and adjust

the reticle. Then insert the polar scope in the polar axis and rotate

the mount axis to check the target remains in the middle of the

reticle. If it doesn't, the polarscope sitting surface is not

perpendicular to the mechanical axis of the mount.



The sitting of the polar scope in the polar axis is not particularly

accurate (mechanically). What I did is to line the polar scope tube

with tape (plus some thin copper plates) in order to adjust the polar

scope in the polar axle by a tight fit on the cilyndrical part of both

pieces rather than relying on a perpendicular (in theory) mating

surface. In this case I do not tight too much the polar scope

tightening ring.



Ok, but that's just me...



Regards



Claudio



--- In Losmandy_users@yahoogroups.com, "Michael Tapper" tapsky@...>

wrote: >

> Jay

>

> I'm happy to report that I got the reticule pretty well centered and

can now move on to other things. >

> I'd like to thank you and all the others who offered help and advise

with this issue. >

> Regards,

> Mike

>

> [Non-text portions of this message have been removed]

>



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